The Northern Knights will be without a match-winner after losing the services of star import James Foster ahead of tonight's HRV Cup match at Seddon Park in Hamilton.

The English wicketkeeper-batsman has been a key contributor in the SkyCity Knights' opening two victories in the domestic Twenty20 competition but has flown home to deal with a family illness.

The Knights hope he will return for the rest of the campaign but said his decision to head back to England was fully supported.

"Our thoughts are with the Foster family at this time and it was not right for James and [wife] Tanya to be on the other side of the world when they needed to be at home," said Northern Districts chief executive David Cooper.

The Knights do have a ready-made replacement in part-time Black Cap BJ Watling.

They were dealt a further blow when Daniel Vettori was ruled out with injury concerns by New Zealand Cricket.

He trained with the Knights this week but NZC medical staff have delayed his return to domestic cricket until December 14. Vettori is recovering from a hernia operation and an Achilles tendon injury.

The defections left Knights coach Grant Bradburn pondering switches to the starting XI at training as they also looked to rectify the minor flaws in the early stages of their campaign.

Foster had been a key performer in the two wins over Otago and Central Districts in partnership with fellow import Steven Croft, giving the heart of the Knights' batting lineup solidity and power, while the Knights bowling has also chiefly been effective.

But Bradburn isn't resting on his laurels, despite giving the opening two matches a tick.

"We're really happy to be winning but we still have a few things to brush up on," Bradburn said.

"Certain parts are going well, others need a bit of effort. It's not too hard to pick out where we've struggled - our start with the bat, and our closing overs with the ball."

The Knights have used Daniel Flynn - now on test duty in Sri Lanka - and Anton Devcich as opening partners to Brad Wilson in their first two matches, while Watling batted at three last weekend when making just one in his return from Sri Lanka.

Veteran seamer Graeme Aldridge has been expensive in both games, but may be given another opportunity with Vettori unavailable.

The Knights lead the standings, with eight points while Canterbury lost their opening match against Wellington by six wickets. However, their side features a host of changes from the XI which opened the Wizards campaign three weeks ago.

Experience paceman Dirk Nannes will feature as their hired gun, with the Australian making a one-off appearance, while Black Caps limited-overs players Andrew Ellis, Tom Latham and Ronnie Hira are all expected to feature.